In a series of experiments, we have shown that ferrous iron of oxyhemoglobin or deoxyhemoglobin is a principal agent in the development of delayed arterial spasm after subarachnoid hemorrhage (SAH). Its mechanism of action is unclear, but a decrease of nitric oxide (NO) levels in the vessel wall, due to the loss of nitric oxide synthase (NOS) from the nervi vasorum, appears to have a central role in the pathogenesis of vasospasm. On the basis of successful reversal and prevention of vasospasm after SAH in primates, we are planning a pilot study of intracarotid infusion of a NO donor in humans for reversal of vasospasm, after preclinical toxicity studies have been completed. Because of the role of oxyhemoglobin as the cause of vasospasm, a chelator of ferrous iron (Fe2+), 2,2'-dipridyl, was tested in its ability to prevent vasospasm in our primate model. Intravenous infusions of the chelator for 14 days was shown to prevent vasospasm in 6 of 7 primates tested with only slight toxicity. This result suggests both a mechanism of and a viable therapy for delayed vasospasm following SAH. Since ferrous iron chelation prevents cerebral vasospasm, we are studying the influence of the ferrous and ferric forms of iron on NO synthase and NO production in astrocytes, smooth muscle cells and endothelial cells, using immunochemistry and an NO probe. We have demonstrated that NO is a free radical scavenger and that administration of it reduces the volume of ischemic cerebral infarction in rats. These results suggested a possible treatment of reperfusion injury after intracarotid thrombolysis. We use a rabbit model of cerebral embolism to study the effects of an NO donor on reperfusion injury. In this experiment we monitor the levels of oxygen free radicals and NO in brain before and during ischemic stroke and then during the reperfusion.